This invention generally relates to ultrasonic testing of railroad rails and further relates to an apparatus and method for maintaining an ultrasonic rail investigating tool in vertical alignment with a rail during testing of that rail. More specifically this invention relates to an apparatus and method that detects the middle of a rail and generates a signal indicative thereof for aligning a rail investigating tool.
Periodic rail maintenance is vital to the normal performance of railway systems and typically includes complicated procedures. Thus, the rail should be inspected for faults and, particularly, for a proper shape, which has to be ascertained to determine whether various rail parameters are within specified acceptable tolerances, or whether the rail should be condemned.
A variety of methods are currently employed to conduct the tests directed to determine external and internal defects of the rails on site. One non-destructive testing method is the ultrasonic testing of a rail. This technique consists in bringing an emitter, receiver or emitter/receiver transducers in contact with the head of the rail, the orientation of which is adapted to the type of flaws to be detected. More particularly, ultrasonic rail testing involves the examination of a wide range of rails some of which have their gauge or head worn down vertically or laterally or both. U.S. Pat. No. 5,419,196 shows one type of ultrasonic testing device for examining a rail.
Ultrasonic transducers used to examine rails may become laterally shifted from the center of the rail so that some transducers employed in the investigating tool are not employed in their optimum position.
During in-situ testing of rails, the transducers typically are mounted on carriages, which roll on top of the rails to maintain the transducers in sonic contact with the rail. Such a testing system includes transducers mounted in a wheel which rolls on the rail, the sonic contact between the transducer and the rolling surface being realized for example by a liquid contained in the wheel as described in U.S. Pat. No. 4,165,648 to Pagano. It is desirable that a proper lateral or transverse positioning of a probe wheel relative to the rail on which the wheel is moved is established for optimum performance.
Techniques for aligning a rail testing carriage on which ultrasonic test equipment is located are known. See, for example, U.S. Pat. No. 4,044,594 to Owens et al. In this patent a rail mounted carriage supports ultrasonic test equipment and is provided with lateral carriage adjustment devices so that the ultrasonic rail test equipment can be maintained in lateral alignment with the rails. This equipment depends upon the use of a guide that runs along the side of the rail gauge to sense its location and thus enable a lateral alignment with respect to that side of the gauge head. This approach depends upon the side of the rail gauge to maintain its normal position relative to the web of the rail. However, if there is wear on that side, lateral adjustment loses its accuracy and alignment becomes less precise.
U.S. Pat. No. 5,020,371 to Panetti (Panetti ""371) describes a device to determine the plane of symmetry of a rail by bouncing ultrasonic pulses off the undersides or fish plates of a rail. This technique assumes that it is independent from wear problems of the head of the rail. However, rails are prone to wear unevenly so that reliance upon the travel times of ultrasonic pulses from the fishplates to derive lateral alignment of the ultrasonic rail testing transducers is prone to errors.
Particularly, Panetti ""371 discloses a method of positioning a member with respect to the symmetry plane of a rail and emitting through the rail""s head two diverging ultrasound beams, each of which is propagated perpendicular to and ricocheted from a respective one of the rail""s fish plates. Upon determining the time difference between the emission and the reception of the echo signal for each of the ultrasound beams and comparing this echo signal with a reference value, a control signal correcting the transverse positioning of the member is generated.
The Panetti system, however, is based on a complicated system of determining and comparing different signals and premised on the notion that the fish plates are perfectly symmetrical to the axis of symmetry of the rail and not subjected to wearing off. As a consequence, the transducers ought to be inclined at the same angle as the fish plates in order to properly determine the deviation from the rail""s axis of symmetry. In reality, however, due to the variations in the dimensions of the rails, misalignment of the abutting ends of the adjacent rails and the angle variation between the fish plates as well as between the transducers, the ultrasonic coupling between the wheel and the rail""s head may not be entirely precise.
U.S. Pat. No. 5,339,692 to Shoenhair et.al discloses a device for locating a web centerline with an array of symmetrically positioned transducers each transmitting and receiving ultrasound signals bounced from either the base or the underside of the rails. The reflected signals are compared to a signal generated by a centrally positioned transducer. As a consequence, if the compared signals have different amplitudes, then a control signal is generated to actuate a means for lateral displacement of a controlling member relative to the rail.
The Shoenhair device has a complicated control system designed to process a plurality of signals, particularly those that bounce from the underside of the rail""s head. As a consequence, the control system may be prohibitively expensive. Also, this device may not be indicative of the actual position of a wheel with respect to the centerline of the rail because transducers receive echoes reflected from a wide segment of the rail including the slanted surfaces of the railhead. To obtain valid information of the wheel""s position with respect to the rail centerline using echoes from the underside surfaces of the railhead, the transducers have to be properly aligned with these surfaces. However, it has been found difficult to achieve such alignment due to variations in the loading of the wheel, variations in the rolling radius of the wheel, the size of the flat and its position relative to transducers positioned above the underside surfaces of the railhead. Furthermore, a heavily loaded wheel has a tendency to act somewhat as a squeegee and force the coupling fluid from the sides of the tread thereby primarily affecting the acoustic coupling between the transducers and the underside surfaces of the railhead.
It is, therefore, desirable to provide an automatic carriage alignment system employing using ultrasonic transducers in a precise and reliable manner.
With an automatic carriage alignment system in accordance with the invention a plurality of ultrasonic beams are obtained from an array of ultrasonic transducers that is laterally aligned transverse to the rail. The beams are formed by selectively pulsing successive predefined groups of ultrasonic elements in the array to produce echo signals from beam reflections from the rail""s base. An echo analyzer responsive to the echo signals is used to derive the lateral position of the array of ultrasonic elements with respect to the centerline of the rail and generate a signal to activate an actuator with which an ultrasonic rail-investigating wheel can then be aligned with the rail.
The reflection analyzer registers signals representative of hits and non-hits from ultrasonic beams with the rail base from successive laterally spaced groups of elements. The hits and non-hits define an edge of the web of the rail and enable one to fix the position of the array relative to the rail. In a preferred mode the center for the array is aligned with the center of the rail. However, other edges can be aligned and if necessary an offset introduced to relate a reference line in the array with a reference line on the rail. A correction signal is generated when the derived lateral position is deemed off-center and is used to correct the lateral alignment of the carriage on which the wheels with their ultrasonic rail investigating transducers are located.
As described in one embodiment of the invention the base hits are detected when an echo signal exceeds a certain threshold. A hit and non-hit data pattern is stored and evaluated to produce a correction signal indicative of the position of the center of the array relative to the centerline of the rail. The correction signal is applied to wheel actuators to displace the carriage so that the centers of ultrasonic wheels used to investigate the rails have a desired alignment with the centerlines of the rails.
As described herein for one embodiment of the invention an initial transducer array control (TAC) provides the electronic circuitry to perform testing of an alignment algorithm and its implementation. The TAC operates ultrasonic transducers in three different modes: constant, scanning and/or alignment.
In the constant mode the TAC may continuously pulse a selected group of N transducers. The scanning pulsing mode is characterized by simultaneously pulsing one (1) through N consecutive transducers of the array, store any hit data in RAM and then pulse N consecutive transducers beginning at transducer 2. The scanning continues until the last N consecutive transducers are pulsed which is particularly useful for calibration purposes. As a result of the calibration, a particular pattern of LEDs can visually inform an operator that the alignment wheel is properly aligned.
In the alignment mode the TAC scans the array to, analyze the data for validity and command a carriage control to move the carriage in accordance with the evaluated data. The alignment algorithm assumes that the center of the array is aligned with the center of the zero degree transducer mounted within each one of two probe wheels, each of which is aligned with a pair of alignment wheels. Other assumptions can be used and can include use of an offset. The key feature is that the array""s position within the probe wheel is known.
It is, therefore, an object of this invention to provide an improved automatic carriage alignment system and method for maintaining a rail investigating tool in lateral alignment with a rail.
It is another object of this invention to provide an automatic carriage alignment system and method that provides a reliable and automatic centering technique for a carriage carrying an ultrasonic rail investigating tool located within a wheel that travels over a rail in proper lateral alignment with the rail.
Yet another object of the invention is to provide an automatic carriage alignment system carrying a rail investigating tool by using those echoes that are reflected from the base of the rail.
Still another object of the invention is to provide an automatic carriage alignment system capable of evaluating echo signals received from the base of the rail in order to generate a control signal to activate a carriage actuator which can laterally displace the carriage to a position which establishes a desired alignment of a rail investigating tool, located on the carriage, with respect to the centerline of the rail.